1. Field of the Invention
This invention relates to bubble domain lattice systems and more particularly to bubble domain lattice systems using multiple layers containing magnetic bubble domains.
2. Description of the Prior Art
A bubble domain system using confined arrays or lattices of bubble domains is described in copending application Ser. No. 395,336, filed Sept. 7, 1973 now abandoned. That application describes systems in which information is stored as magnetic bubble domains which occupy every bit position. Consequently, it is necessary to code information in terms of the various magnetic properties of the bubble domains themselves. For instance, one type of coding technique which is described in the above-mentioned copending application utilizes different states of wall magnetization rotation of the bubble domains. Depending upon the state of rotation of the wall magnetization of the domains, the domains can be made to deflect in different directions in a gradient magnetic field. In addition to this type of coding, other types of coding are described in that copending application.
It is sometimes difficult to code magnetic bubble domains in accordance with their magnetic properties although such coding has been demonstrated. For instance, considerable circuitry may be required and a statistical distribution of bubbles having various properties may be obtained, from which certain bubbles have to be selected. Phenomena such as dynamic conversion (i.e., change of wall configuration during wall motion) must be guarded against. Accordingly, the present invention seeks to provide a bubble domain lattice system in which information states can be coded in the conventional way (namely, the presence and absence of these domains). In order to do this, multiple magnetic layers are provided in which a complete lattice is present in one layer, while only the information bubble domains (bubbles and voids) are present in the second magnetic layer. Movement of the bubble domains in the lattice causes movement of the information domains in the adjacent magnetic layer. These information domains can be generated and sensed by conventional techniques.
Mutual interaction between bubble domains in different magnetic sheets has been described previously. For instance, reference is made to the Conference Proceedings of the American Institute of Physics, Proc. No. 5, 17th Annual Conf. on Magnetism and Magnetic Materials, Chicago, Ill., pg. 135. This reference article discusses movement of bubble domains in one magnetic sheet by a dragging effect due to a magnetostatically coupled bubble domain in a second magnetic sheet. Another article of interest is contained in Philips Research Reports, Vol. 27, No. 1, pg. 7, February 1972. In this reference, bubble domains in different magnetic media are magnetostatically coupled, and it is stated that an extreme case is that where a lattice of bubble domains is present in one of the magnetic sheets. This reference discusses crosstalk due to this magnetostatic coupling and seeks to minimize the adverse effect of this crosstalk. That is, it is not desired to utilize the magnetostatic coupling between bubble domains in two magnetic sheets, but rather to study the amount of crosstalk which results from such coupling, with a view toward designing systems where such coupling is minimal.
Another article of interest is that of Y. S. Lin, E. A. Giess, and P. J. Grundy, which appeared in Applied Physics Letters, Vol. 23, p. 485, 1973. This article also discusses two layer bubble domain structures.
Accordingly, it is a primary object of the present invention to provide bubble domain lattice systems in which conventional coding can be utilized.
It is another object of this invention to provide bubble domain lattice systems where the bubble domains in the lattice do not have to be coded in terms of their magnetic properties.
It is a further object of this invention to provide multiple layer bubble domain lattice systems.
It is another object of this invention to provide high density bubble domain lattice systems using coding in terms of presence/absence of bubble domains.
It is still another object of this invention to provide techniques for high density storage using magnetically coupled bubble domain pairs.